KITTERY, Maine — The USS Miami, the nuclear submarine damaged by a fire earlier this year, will remain at Portsmouth Naval Shipyard will it undergoes repairs now estimated at $450 million.

The U.S. Navy announced Wednesday it hopes to have the submarine operational by April 2015, with a goal of returning it to the fleet for another decade.

The resources and workforce required to support the repairs will come from Portsmouth Naval Shipyard, the private sector and from workers in surrounding communities in New Hampshire and Maine, according to a Navy announcement.

Also assisting in the repairs will be ship-building experts from Electric Boat in Groton, Conn., and Huntington Ingalls Industries in Newport News, Va., according to information provided by the office of U.S. Sen. Susan Collins, R-Maine.

Navy officials announced their decision to carry out the costly repairs late last week, ending speculation about whether the Miami would be salvaged.

Built for $900 million, the USS Miami (SSN 755) was scheduled to remain in service for another nine or so years before the fire broke out. The Miami is among the older boats in a fleet of about 54 U.S. attack submarines, which are used to launch missiles, gather intelligence and support other Navy vessels.

The USS Miami fire, which erupted on May 23, continued to burn for 12 hours before it was brought under control. Shipyard firefighters and dozens of others from around the Seacoast, and from as far away as Massachusetts and Connecticut, helped in the effort.

Casey James Fury, a 24-year-old civilian worker at the shipyard, has been charged with arson for allegedly starting the fire. Investigators say Fury lit a pile of rags on fire while working inside the ship in hopes of creating an emergency that would allow him to leave work early.

Fury is also accused of setting a second fire underneath the Miami several weeks later.

Fury was ordered held without bail on Aug. 1 as he awaits a grand jury indictment in federal court in Portland, Maine.

In June, the Navy authorized workers to continue overhauling parts of the ship that were not damaged in the fire. The Miami was three months into a scheduled 20-month overhaul at the time of the May blaze.

Work is now continuing to clean the interior, rip out areas damaged by fire and water and complete a technical assessment of the damage. The Navy is also developing a strategy for the repair work and refining the cost estimate.

On Wednesday, the Navy announced it expects to award an advanced planning contract in September that will bring in engineers to plan the repair work and begin procuring material. A contract for the repair work is set to follow in spring 2013.

The Navy had originally pegged the cost of the repairs at between $400 million and $440 million. The number was upped to $450 million Wednesday in the latest announcement from the Navy. The price tag includes 10 percent variability due to the "unique nature of the repair" and the cost of changing the maintenance schedule for other ships, according to the Navy.

Collins said Wednesday she is "thrilled" at the Navy's decision to fix the ship and authorize a "significant investment in our national security."

"Portsmouth Naval Shipyard has the best submarine repair capability in the nation, and with the expert assistance of both Electric Boat and Huntington Ingalls, the Miami will be repaired swiftly and will provide the Navy with many years of additional service," said Collins, a member of the Senate Armed Services Committee, in a written statement.

In July, the Navy folded three separate investigations into the fire under the authority of an oversight board. The board is composed of three-star flag officers from Naval Sea Systems Command, Commander Naval Installations Command and Commander Submarine Forces, according to the Navy.

The board is continuing to study the May 23 fire in hopes of deriving lessons from the incident and developing corrective actions.